Sulfur and metal compounds removal in petroleum refining is accomplished with the aid of a catalyst of a Group VI B metal compound and an iron group metal compound on a support of porous refractory oxide material. A coating of oxides of cobalt or nickel and molybdenum or tungsten on gamma alumina particles, which are converted to sulfides prior to use, is the type and form of such hydrodesulfurization and hydrodemetallization catalysts long widely used in the industry. The rate of increase in catalyst consumption has grown with both the trend toward greater refining production volume and increasing use of high-sulfur/high-metal crude oil and refinery feed stock. Resulting accumulation of such catalyst in spent condition has for some time been generally recognized to constitute an escalating solid toxic waste disposal problem.
The typical range of analysis for these spent catalysts is:
______________________________________ Major Constituents % ______________________________________ Mo 0-10 W 0-15 Ni 0-3 Co 0-3 V 0-15 Fe 0-3 Al.sub.2 O.sub.3 30-60 SiO.sub.2 0-4 TiO.sub.2 0-5 P.sub.2 O.sub.5 0-5 S total 3-15 Carbon total 3-25 Free Oil 0-15 ______________________________________ Minor Constituents P.P.M. ______________________________________ As up to 2000 Cu, Zn, Cr up to 1000 Pb, Mn up to 500 ______________________________________
The spent catalysts have also been seen as a potential major source of metal values, particularly cobalt, a strategic metal unavailable in necessary quantities from domestic or secure foreign primary sources. As a consequence, there have been many efforts by others for more than a decade to devise a solution to this problem either by decontaminating spent catalyst and restoring it to usable condition or by disintegrating it and recovering at least some of its metal values.
The large number of major and minor constituents in the spent catalyst, mostly which are soluble to some degree in conventional lixivants for selective leaching, make recovery of the commercially interesting metals (i.e. Mo, W, Ni, Co, V, Al) in pure compound form a very difficult task. To the best of our knowledge, only limited success along such lines has hitherto been achieved and this kind of waste product continues to accumulate for lack of an adequate commercially feasible means or procedure for treating it either for recovery or disposal.